Light weight tubular columns

ABSTRACT

A method of forming a light weight tubular column and a column formed by the method, wherein firstly a tubular member is extruded to have a series of circumferentially spaced beads joined by webs, slots are then pierced in the webs to form the beads into free portions which are interconnected with one another by the web portions remaining between the slots, and then the circumference of the tubular member is increased by passing the expanding tool through the member so as to increase the lengths of the free portions of the beads thus forming a trusslike configuration, without fabrication.

[ 1 Oct. 311, 1973 1 1 LIGHT WEIGHT TUBULAR COLUMNS [75] Inventor: Harold Rex Jury, Norwood,

Australia [73] Assignee: Jury & Spiers Proprietary Limited,

Norwood, South Australia, Australia 22 Filed: Dec. 29, 1971 21 Appl. No.: 213,506

[30] Foreign Application Priority Data 2/1917 Riceetal ..29/155C 2,141,642 12/1938 Cross .1 29/155 R X 3,564,688 2/1971 DeGain 29/155 R Primary ExaminerThomas H. Eager Att0rney-Albert H.0ldham et al.

57 ABSTRACT A method of forming a light weight tubular column and a column formed by the method, wherein firstly a tubular member is extruded to have a series of circumferentially spaced beads joined by webs, slots are then pierced inthe webs to form the beads into free portions which are interconnected with one another by the web portions remaining between the slots, and then the circumference of the tubular member is increased by passing the expanding tool through the member so as to increase the lengths of the free portions of the beads thus forming a truss-like configuration, without fabrication.

5 Claims, 6 Drawing Figures rmmmnmaoms 3.768.130

SHEET 10? 3 LIGHT WEIGHT TUBULAR COLUMNS This invention relates to a method of forming a light weight tubular column.

BACKGROUND OF THE INVENTION It is generally recognised in the art that the greatest rigidity can be obtained in a column for a given mass of material if the column is in the form of a triangularly braced structure, that is, a structure comprising a plurality of short struts jointed together at their extremities by chords to form a series of triangles. The art is well developed and much information is available on the strength of braced columns and the structural requirements of each of the struts.

These columns are usually constructed by a fabrication process, and are cumbersome and expensive members to fabricate, the structure if being welded usually being built on a former, the length of each strut and the shape of the mating ends being important. The amount of labour in the shaping of the ends is considerable, and accordingly some structures are built up by bolting or riveting joints, but these have been found even more costly to fabricate.

A panel of so-called expanded metal" is a panel which is formed by slitting a sheet of metal with a series of rows of slits, each slit being staggered with respect to a pair of adjacent slits in an adjacent row and the distance between the ends of the adjacent slits being less than the length of the staggered slit so that the metal between the slits is flanked onboth sides by the slits for portions of its length, the sheet subsequently being reduced in length and increased in width so that the metal is bent to a shape and usually twisted from the'plane originally occupied by it. This material is unsuitable for structural loading because of the failure to retain a coplanar shape, and because of the tendency for the slits to split at their ends. Even if expanded metal is utilised in the structure of a tubular column, it requires the addition of longitudinally extending chords, the expanded metal being an unnecessarily expensive and heavy intermediate bracing between the chords.-Thus the use of the expanded metal panels of the abovementioned type are unsuitable for columns.

Certain proposals have been put forward, as for example in the US. Pat. No. 1,215,061, wherein the expanded metal process is substantially used, excepting that the slits are made in the walls of a tubular member which is afterwards expanded. This process avoids the difficulty of'the 'metal struts being twisted out of their proper plane, but still results essentiallyv in .a column which is devoid of longitudinally extending chords. Such a column is easily bent when subjected to side loadings, and the configuration of its walls is essentially unsound from an engineering point of view. It is still open to the objection that the ends of the slits tend to split, and it is open to a further difficulty not encountered with the normal expanded metal process, that of the lancing a series of slits in the walls of a tubular member. The walls are inherently stiff in a direction transverse to the direction of the slits, and lancing can only be achieved by distortion of the metal. Furthermore an internal die of high cost is necessary for backup purposes during the lancing operation.

OBJECT OF THE INVENTION The main object of this invention is to provide a process for the forming of a light weight tubular column without fabrication, which when used can provide a tubular column having superior mechanical strength, in that the method makes possible the construction of a tubular column with longitudinally extending chords. A further object is to-provide a process the use of which will make it possible to greatly reduce the tendency for the ends of the openings to split. A still further object is to provide a process wherein the piercing operation can be effected with low cost tooling and at a relatively high speed.

SUMMARY OF THE INVENTION In general, the invention relates to a method of forming a column. The method includes the steps of extruding a tubular member having spaced webs and beads in its'walls, piercing slots in they webs, and passing an expanding tool through the tubular member in such a way as to increase the lengths 'of some or all of the beads and simultaneously increase the circumference of the extruded member, while the column so formed has those beads the lengths of which are increased inclined to respective radial planes, and strained beyond their yield points so as to increase stiffness.

More specifically, the characterising features of the method of the invention are the steps a. extruding a tubular member of circumference less than the circumference of the column to be formed, the cross-sectional configuration of the tubular member including a series of circumferentially spaced beads joined by webs,

b. piercing a series of longitudinally extending rows of slots in the webs, each slot having curved ends, each slot being staggered with respect to a pair of adjacent slots in an adjacent row, the web portions remaining between the ends of said adjacent slots constituting a joining web between adjacent beads which is less than the length of said staggered slot whereby the bead between those slots is flanked on both sides by slots for portions of its length, and

c. increasing the circumference of said tubular member by passing an expanding tool throughthe member so as to increase the lengths of these portions of the beads flanked on both sides by slots.

A light weight, tubular column formed by the above method comprises a unitary member having a series of beads each extending from end to end of the column, each bead having on each side thereof a series of spaced joining webs joining it to a pair of adjacent beads, some at least of the beads having those portions between adjacent joining webs inclined toa plane extending radially from the central longitudinal axis of the column, the inclined portions being in a condition of having been strained beyond their yield points.

- By means of this'invention, the slots may be pierced to provide any one of a plurality of configurations, including a configuration in which all of the beads are inclined to the longitudinal axis and a configuration in which some of the beads are parallel to the longitudinal axis so as to form longitudinally extending chords. If the slots have curved ends, it will be seen that the stress concentration is considerably reduced and therefore the danger of splitting at the ends of the slots is less than if slits only are used. This in turn enables the process to be used wherein the beads which are inclined to the longitudinal axis of the column are in a condition of having been strained during the process of expanding the circumference of the column, not merely having been bent. This has the effect of work hardening the metal thus making it stiffer so that the column will become more rigid, and enables the inclusion in a column of longitudinally extending chords which lie in a plane extending radially from the central longitudinal axis of the column. This latter feature for columns which are to withstand heavy side loadings is not possible to achieve with the prior art methods.

A still further advantage of the invention is that the webs may be intermediate the inner and outer edges of the beads which may be supported on a simple circular mandrel when the webs are pierced.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention is described hereunder in some detail with reference to and is illustrated in the accompanying drawings in which:

FIG. 1 is a diagrammatic representation illustrating the means for piercing an extruded tubular member,

FIG. 2 is an enlarged view showing the manner in which the slots are pierced upon closure of the punches on the tubular member of FIG. 1,

FIG. 3 shows diagrammatically the process of passing an expanding tool through the member so as to increase the lengths of those portions of the beads which are flanked by the slots, FIG. 3 illustrating a configuration resulting from increasing the circumference of the tubular member of FIGS. 1 and 2, which will have inclined beads only,

FIG. 4 is a fragmentary projection onto a flat plane of a tubular member according to a second embodiment, after having been pierced but before the circumference has been increased,

FIG. 5 is a fragmentary elevation ofa tubular column after expansion of a tubular member having the pattern of slots illustrated in FIG. 4, and

FIG. 6 is a section taken on line 6-6 of FIG. 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS Referring first to the embodiment of FIGS. 1 and 2, a tubular member 10 is formed by the process of extrusion of extrusile metal to have a cross-sectional configuration which includes a series of circumferentially spaced beads 11 which are separated by webs 12. The extrusile metal can conveniently be aluminium, an aluminium alloy, or a copper base alloy, but requires to have properties which will allow it to be strained by an amount sufficient to give the required inclination to the struts subsequently to be formed.

A difficulty can be encountered if an attempt is made to pierce the webs individually, in that only a small degree of backup exists when, say, the last series of webs is to be pierced around the circumference of the tubular member, and firstly to obviate this difficulty and secondly to provide higher production speeds, the tubular member 10 is surrounded with a series of hydraulic cylinders 15, the piston rods 16 of each having attached thereto a punching die 17, each punching die 17 being radially aligned with a respective web 12.

The webs 12 are positioned intermediate the radially inner and outer surfaces of the respective beads 11, and the tubular member 10 is retained by means of a central mandrel 18, the central mandrel 18 supporting the inner surfaces of the beads 11, so that there exists a series of longitudinally extending slots between the surface of the mandrel 18 and the inner surfaces of the webs 12. These slots provide an accommodation space for the slugs 19 which are pierced so as to form the series of slots in the tubular member. The configuration which is illustrated in FIGS. 1 and 2 will result in a pierced member as shown in FIG. 3, and after expansion of the. tubular member, the column so formed will have no longitudinally extending chords.

The slots are arranged to be long compared with the spacing between their ends, and the ends of the slots are curved in shape. If the slots are long and each slot is staggered with respect to a pair of adjacent slots in an adjacent row, and the distance between the ends of said adjacent slots is less than the length of the staggered slot, each of the beads between the slots is then flanked on both sides by slots for portions of its length.

The next stage in the method of forming the light weight tubular column is to increase the circumference of the tubular member by passing an expanding tool through it. The expanding tool can be of known type, for example, of the type wherein a series of segments are driven radially outwardly by longitudinal movement of a tapered expander, but in the arrangement shown in FIG. 3, the expanding tool is a mandrel 22 on the end of a tension bar 23, and a draw bench (not shown) of conventional type is employed. This ensures straining of the beads so that expansion does not take place merely by bending.

FIG. 4 illustrates a projection onto a flat plane of an arrangement of alternate major and minor beads which gives the configuration illustrated in FIGS. 5 and 6 when the circumference of the tubular member is increased. The major beads are all designated 25 (there being eight in all but four only shown in FIG. 4) and the minor beads are designated 26. They are interconnected by webs 27, the webs 27 being pierced with slots 28 in the pattern shown. It will be seen that the pattern of slots 28 is such that each slot is staggered with respect to a pair of adjacent slots in the adjacent row which is separated by a minor bead, and that the distance between the ends of the adjacent slots is less than the length of the said staggered slot so that the minor bead between the slots is flanked on both sides by the slots for portions of its length. However it will be noted also that the slots are not staggered with respect to the slots of an adjacent row separated by a major bead. If the slots are not staggered, upon increase of the circumference of the tubular column, there is no force tending to change the shape of the major beads, so that the major beads become the longitudinally extending beads or chords of the product which is illustrated in FIG. 5, and lie within radial planes. The minor beads however become strained beyond their yield point to for the struts which are also designated 26 in FIGS. 5 and 6, and are inclined to respective radial planes. When the minor beads 26 are stretched to become the webs 27 as shown in FIG. 6, the slots 28 become triangular openings 29.

What I claim is:

1. A method of forming a light weight tubular column comprising the steps:

a. extruding a tubular member of circumference less than the circumference of the column to be formed, the cross-sectional configuration of the tubular member including a series of circumferentially spaced beads joined by webs,

b. piercing a series of longitudinally extending rows of slots in the webs, each slot having curved ends, each slot being staggered with respect to a pair of adjacent slots in an adjacent row, the web portions remaining between the ends of said adjacent slots constituting a joining web between adjacent beads which is less than the length of said staggered slot whereby the bead between those slots is flanked on both sides by slots for portions of its length, and

. increasing the circumference of said tubular member by passing an expanding tool through the member so as to increase the lengths of these portions of the beads flanked on both sides by slots.

2. The method according to claim 1 wherein the expanding tool is a mandrel,- and further comprising moving the mandrel through the tubular member on a draw bench.

3. The method according to claim 1 wherein the tubular member is extruded with said beads spaced equally around its circumference, and each slot is so pierced as to be staggered with respect to a pair of adjacent slots in each of two adjacent rows, whereby the length of each said bead is increased.

4. The method according to claim 1 further comprising so piercing a plurality of rows of slots that each slot in a plurality of rows is staggered with respect to a pair of adjacent slots in one only of the adjacent rows, but aligned with a slot in the other adjacent row, whereby when the circumference of said tubular member is increased the lengths of only those beads which lie between said rows of said staggered slots are increased.

5. The method according to claim 4 wherein said tubular member is extruded to have major and minor beads, the major beads being greater in cross-sectional area than the minor beads, adjacent major beads having at least one minor bead therebetween, the slots on each side of each minor bead being staggered and the slots on each side of each major bead being aligned.

Patent Dated October 30, .1973

r S Lii nli R21?! 9. .3

It is certifivd that error appears in the above-identified patent and that mid Letters Patent are hereby corrected as shown be] ow:

Column 1, Line 1 1, change "jointed" to joined Column 4, line 56,- change "for! to form Signed and sealed this 9th day of April 197M;

(SEAL) Attest: I 7

EDWARD M.FLETCHER JR. G. MARSHALL DANN Attesting Officer Commissioner of Patents 

1. A method of forming a light weight tubular column comprising the steps: a. extruding a tubular member of circumference less than the circumference of the column to be formed, the cross-sectional configuration of the tubular member including a series of circumferentially spaced beads joined by webs, b. piercing a series of longitudinally extending rows of slots in the webs, each slot having curved ends, each slot being staggered with respect to a pair of adjacent slots in an adjacent row, the web portions remaining between the ends of said adjacent slots constituting a joining web between adjacent beads which is less than the length of said staggered slot whereby the bead between those slots is flanked on both sides by slots for portions of its length, and c. increasing the circumference of said tubular member by passing an expanding tool through the member so as to increase the lengths of these portions of the beads flanked on both sides by slots.
 2. The method according to claim 1 wherein the expanding tool is a mandrel, and further comprising moving the mandrel through the tubular member on a draw bench.
 3. The method according to claim 1 wherein the tubular member is extruded with said beads spaced equally around its circumference, and each slot is so pierced as to be staggered with respect to a pair of adjacent slots in each of two adjacent rows, whereby the length of each said bead is increased.
 4. The method according to claim 1 further comprising so piercing a plurality of rows of slots that each slot in a plurality of rows is staggered with respect to a pair of adjacent slots in one only of the adjacent rows, but aligned with a slot in the other adjacent row, whereby when the circumference of said tubular memBer is increased the lengths of only those beads which lie between said rows of said staggered slots are increased.
 5. The method according to claim 4 wherein said tubular member is extruded to have major and minor beads, the major beads being greater in cross-sectional area than the minor beads, adjacent major beads having at least one minor bead therebetween, the slots on each side of each minor bead being staggered and the slots on each side of each major bead being aligned. 